The present invention relates to the general field of nozzles with confluent streams fitted to turbine engines.
Typically, a turbine engine nozzle with confluent streams comprises an annular central body centered on a longitudinal axis of the engine, an annular core cowl positioned around the central body, being on the same axis, so as to co-operate therewith to define a core channel, and an annular bypass cowl positioned around the core cowl, being on the same axis, so as to co-operate therewith to define a bypass channel.
A gas stream (referred to as a core stream or hot stream) coming from the low pressure turbine of the engine flows in the core channel of the nozzle. Another gas stream (referred to as the bypass stream or the cold stream) outside the engine flows in the bypass channel. The core and bypass streams mix in a confluence zone situated at the exit from the core channel. Reference may be made to Document EP 1 870 588, which describes a mixer for such a nozzle.
A nozzle with confluent streams presents certain problems relating to questions of ventilation at different operating points of the engine. In particular, the nacelle of the engine is ventilated by a stream of air flowing in the bypass channel and that is sucked in by the core stream in the confluence zone by a jet pump effect. Unfortunately, one of the critical points of that system of suction by the jet pump effect is how it operates when the engine is idling. When idling, the jet of the core stream is reduced and is therefore not sufficiently energetic to ensure that the ventilation flow is driven correctly. Such poor suction can even lead to hot gas being ingested into the bypass channel, and that can lead to severe damage for equipment present in the nacelle compartment and indeed for the nacelle itself.
In order to avoid that phenomenon of re-ingesting hot gas, it is possible to improve the mixing between the core stream and the bypass stream. One known solution is to position geometrical elements that generate vortices in the primary channel in the proximity of the confluence zone. Such vortex generators serve to increase the amount of turbulence, thereby enhancing mixing between the streams. Nevertheless, in cruising flight, the vortex generators lead to significant head loss, with direct consequences on the overall efficiency of the engine.
Furthermore, those problems of re-ingesting hot gas while idling and of head loss while cruising are made worse by the residual gyration of the core stream on entry into the nozzle. Depending on the operating speed of the engine, the core stream entering into the nozzle possesses an azimuth speed component that is not zero. This residual gyratory motion is generally not in the same direction while the engine is operating at idling speed and while it is operating at cruising speed. Unfortunately, this azimuth component has the consequences both of increasing the probability of hot gas being re-ingested while idling, and of mismatching the vortex generators at cruising speed (thereby increasing head losses).